Rename `integrate.rake` to `generate_data.rake`.

- Rename `integrate.rake` to `generate_data.rake`.
- Rename task name from `test` to `gen_data`.

This commit refs #59.
Refine the `git` command line usage.

This commit refs #59.
Specify 2 branch/hash value, when using `git diff`.

- `git diff` master to current_branch.

This commit refs #59.
Divide the common function to retrieve branches from the main procedures.

This commit refs #59.
Merge pull request #59 from kazu634/id/59

Rakefileを改善する